Hair, a filamentous outgrowth of protein found only on mammals, is integral to our body image and can have a profound influence on our self-esteem and self-confidence. The hair of non-human mammal species is commonly referred to as fur. In some species, hair is absent at certain stages of life.
Hair grows from hair follicles deep in the dermis and projects from the epidermis of the skin. Human skin has two types of hair: vellus hair and terminal hair. Much of human hair is short, underpigmented vellus hair rather than terminal hair. The most noticeable part of human hair is the hair on the head, which can grow longer than on most mammals and is more dense than most hair found elsewhere on the body. The term “scalp” refers to the integument of the upper part of the head, usually including the associated subcutaneous structures. The scalp is the anatomical area bordered by the face anteriorly and the neck to the sides and posteriorly.
Vellus hair is short, fine, “peach fuzz” body hair. It is a very soft, generally pale, and short hair that grows in most places on the human body in both sexes. It is usually less than two cm long and the follicles are not connected to sebaceous glands. It is most easily observed in women and children, as they have less terminal hair to obscure it. It is also found in pre-adolescents and in male pattern baldness.
Terminal hair is developed hair, which is generally longer, coarser, thicker and darker than the shorter and finer vellus hair. Phases of growth in terminal hair are more apparent than in vellus hair; it generally has a longer anagen phase. It has associated sebaceous glands, whereas a vellus hair may not. Under certain conditions, such as puberty, some vellus hair may become androgenic hair. Under other conditions, such as male pattern baldness, it may revert to a vellus-like state.
Each hair comprises two structures: the follicle in the skin and the shaft we see. The follicle contains several layers. At the base of the follicle is a projection called a papilla, which contains capillaries, or tiny blood vessels, that feed the cells. The living part of the hair, the area surrounding the papilla called the bulb, is the only part fed by the capillaries. The cells in the bulb divide every 23 to 72 hours, faster than any other cells in the body. The follicle is surrounded by two sheaths—an inner and outer sheath. These sheaths protect and mold the growing hair shaft. The inner sheath follows the hair shaft and ends below the opening of a sebaceous (oil) gland, which produces sebum, a natural conditioner and sometimes an apocrine (scent) gland. The outer sheath continues all the way up to the gland. An erector pili muscle attaches below the gland to a fibrous layer around the outer sheath. When this muscle contracts, it causes the hair to stand up.
The primary component of the hair fiber is keratin. Keratins are proteins, long chains (polymers) of amino acids. The hair shaft contains three layers of keratin. The inner layer, which is called the medulla, may not be present. The next layer is the cortex, which makes up the majority of the hair shaft. The outer layer is the cuticle, which is formed by tightly packed scales in an overlapping structure similar to roof shingles. Most hair conditioning products attempt to affect the cuticle. Pigment cells are distributed throughout the cortex and medulla giving the hair its characteristic color.
The term “eyebrow” refers to an area of coarse skin hairs above the eye that follows the shape of the brow ridges. The main function of the eyebrow is to prevent moisture, mostly salty sweat and rain, from flowing into the eye, an organ critical to sight. The typical curved shape of the eyebrow (with a slant on the side) and the direction in which eyebrow hairs are pointed, make sure that moisture has a tendency to flow sideways around the eyes, along the side of the head and along the nose. Eyebrows also prevent debris such as dandruff and other small objects from falling into the eyes, as well as providing a more sensitive sense for detecting objects being near the eye, like small insects. Eyebrows also have an important facilitative function in communication, strengthening facial expressions such as surprise, confusion, or anger.
The terms “eyelash” and “lash” are used interchangeably to refer to one of the hairs that grow at the edge of the eyelid. Eyelashes protect the eye from debris and provide a warning that an object (such as an insect or dust mite) is near the eye (which then is closed reflexively).
The inside of the nose contains small hairs called cilia. These cilia and nasal mucus clean the air drawn into the nose of the microscopic particles we inhale, including dust, pollen, and pollutants, for ultimate passage to the lungs.
Hair Biology
There are three stages of hair growth: catagen, telogen, and anagen.
Anagen is the active growth phase of the hair during which the cells in the root of the hair are dividing rapidly. Anagen hairs are anchored deeply into the subcutaneous fat and cannot be pulled out easily. When a new hair is formed, it pushes the club hair up the follicle and eventually out. During this phase the hair grows about 1 cm every 28 days. Scalp hair stays in this active phase of growth for 2-6 years. Human subjects that have difficulty growing their hair beyond a certain length have a short active phase of growth. Human subjects that have very long hair have a long active phase of growth. The hair on the arms, legs, eyelashes, and eyebrows have a very short active growth phase of about 30-45 days, which is why they are so much shorter than scalp hair.
The anagen phase is followed by a catagen phase. The catagen phase is a transitional stage that lasts for about 2-3 weeks. About 3% of all hairs are in this phase at any time. During this time growth stops and the outer root sheath shrinks and attaches to the root of the hair. This is the formation of what is known as a club hair.
After catagen, the hair goes into a telogen phase. Telogen is the resting phase, which accounts for 10-15% of all hairs. It lasts for about 100 days for hairs on the scalp and much longer for hairs on the eyebrow, eyelash, arm and leg. During this phase the hair follicle is completely at rest and the club hair is completely formed. As compared with anagen hair, telogen hair is located higher in the skin and can be pulled out relatively easily. Pulling out a hair in this phase will reveal a solid, hard, dry, white material at the root. Normally, about 25-100 telogen hairs are shed each day.
In the normal scalp, approximately 80 to 90 percent of follicles are growing (anagen), about 5 to 10 percent are resting (telogen), and 1 to 3 percent are undergoing involution (catagen). Each day up to 75 hairs in telogen are shed from the scalp and about the same number of follicles enter anagen.
The term “alopecia” is a medical term for the absence or loss of hair including eyelashes, eyebrows, and scalp hair, as a result of illness, functional disorder, or hereditary disposition. For example, the term “Alopecia adnata” refers to underdevelopment of the eyelashes. Alopecia frequently occurs in patients undergoing treatment for cancer or suffering from other diseases, such as AIDS, where cell-killing, or cytotoxic, drugs are used.
Hair loss typically is categorized as scarring or nonscarring. Scarring alopecia, also known as “cicatricial alopecia”, refers to a collection of hair loss disorders that may be diagnosed in up to 3% of hair loss patients. It occurs worldwide in otherwise healthy men and women of all ages. While there are many forms of scarring alopecia, the common theme is a potentially permanent and irreversible destruction of hair follicles and their replacement with scar tissue. Examples include bullous diseases, chemical alopecia, discoid lupus erythematosus, folliculitis (severe), lichen planopilaris, dissecting cellulitis, and tumors.
The term “nonscarring alopecia” refers to hair loss without permanent destruction of the hair follicle. Examples include anagen effluvium, androgenetic alopecia, chemical alopecia, folliculitis (mild), inherited disorders of the hair shaft, telogen effluvium, alopecia areata, and traumatic alopecia.
The term “anagen effluvium” refers to the hair loss associated with chemotherapeutic agents that cause immediate destruction and release of anagen hair.
The term “androgenic alopecia” refers to a gradual decrease of scalp hair density in adults with transformation of terminal to vellus hairs, which become lost as a result of familial increased susceptibility of hair follicles to androgen secretion following puberty. The most common form of androgenic alopecia is male pattern baldness. The most common form of androgenic alopecia in women is female pattern alopecia, a diffuse partial hair loss in the centroparietal area of the scalp, with preservation of the frontal and temporal hairlines. When it occurs in females, it is associated with other evidence of excessive androgen activity, such as hirsuitism.
The term “telogen effluvium” refers to a condition resulting from an abrupt shift of large numbers of anagen hairs to telogen hairs on the scalp, with a corresponding change in the ratio of anagen hair to telogen hair from the normal ratio of 90:10 to 70:30. This form of alopecia generally begins approximately 3 months after a major illness or other stress (e.g., surgery, parturition, rapid weight loss, nutritional deficiency, high fever, or hemorrhage) or hormonal derangement; it also has been reported after the initiation of treatment with certain medications.
The term “alopecia areata” refers to a common condition of undetermined etiology characterized by circumscribed, nonscarring, usually asymmetrical areas of baldness on the scalp, eyebrows, and beaded portion of the face. Hairy skin anywhere on the body may be affected. It is thought to be an autoimmune disease occurring on areas of the body (most commonly the scalp) where the person's immune system attacks hair follicles, thereby suppressing and arresting hair growth.
Those suffering from hair loss often experience embarrassment and the fear being ridiculed by others because they look different. Some may take to wearing oversized eyeglasses in an attempt to hide the absence of eyelashes and/or eyebrows. Loss of nasal cilia may render some more susceptible to respiratory illnesses.
Current therapies for hair loss are designed primarily for scalp applications. These include topical minoxidil (Rogain®), antiandrogen agents, including the androgen-receptor blockers sprionolactone, cyproterone acetate, and flutamide, and the 5α-reductase inhibitor finasteride (Propecia®, Merck & Co.), preparations of progresterone and/or estrogen, and hair transplantation.
Prostaglandins are a family of a group of lipid compounds that are derived enzymatically in the body from essential fatty acids. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring. Prostaglandins have a wide variety of effects, including, but not limited to, muscular constriction, mediating inflammation, calcium movement, hormone regulation and cell growth control. Prostaglandins act on a variety of cells, including vascular smooth muscle cells (causing constriction or dilation), platelets (causing aggregation or disaggregation), and spinal neurons (causing pain).
Scientists stumbled on the hair thickening properties of prostaglandin F2α analogs while researching their use as an intraocular pressure (IOP)-lowering drug for use in patients with glaucoma and ocular hypertension. Prostaglandin F2α analogs have the following general chemical structure wherein the dashed bonds represent a single or double bond which can be in the cis or trans configuration:

For example, latanoprost [(1R,2R,3R,5S)3,5-dihydroxy-2-[(3R)-3-hydroxy-5-phenylpentyl]cyclopentyl]-5-heptenoate], marketed by Pfizer as Xalatan® is a prostaglandin analog in which R is H, B is —CH2—, n is 0, X is OCH(CH3)2, and the dashed bonds represent a double bond. See U.S. Pat. No. 6,262,105, issued to Johnstone. Although Johnstone reported the stimulating effect of this drug on eyebrow and eyelash hair growth and pigmentation, Latanoprost works poorly on eyelashes.
Another example, is bimatoprost (cyclopentane N-ethyl heptenamide-5-cis-2-(3α-hydroxy-5-phenyl-1-trans-pentenyl)-3,4-dihydroxy, [1α,2β,3α,5α], sold by Allergan, Inc. of Irvine, Calif. as Lumigan®, a 0.03% ophthalmic solution for treating glaucoma. Bimatoprost is a prostaglandin analog in which R is H, B is —CH2—, n is 0, X is NHC2H5 and the dashed bonds represent a double bond (U.S. Published Application No. 2003/0147823). Bimatoprost, which also has been found effective to increase the growth of eyelashes when applied in the FDA approved manner, dissolves best for use on eyelashes but has negative side effects, such as, for example, redness and discoloration along the periocular skin; eye irritation; and foreign body sensation. In addition, bimtoprost has the highest incidence of hyperemia.
Another synthetic prostaglandin analog used for treatment of glaucoma is isopropyl (Z)-7-[(1R,2R,3R,5S)-3,5-dihydroxy-2-[(1E,3R )-3-hydroxy-4-[(α,α,α-trifluoro-m-tolyl)oxy]-1-butenyl]cyclopentyl]-5-heptenoate, or Travaprost (TRAVATAN® Alcon), which is available as a 0.004% ophthalmic solution. Travoprost is a prostaglandin analog in which R is H, B is O, Y is CF3, X is OCH(CH3)2, and the dashed bonds represent a double bond. Travaprost does not work well for eyelash growth, taking longer than other like products.
Therefore it is an object of the present invention to provide prostaglandin analogs that will promote appropriate hair growth when applied topically to subjects in need thereof without causing significant undesirable side effects.